The issue with spin-gravity is angular momentum. The smaller you want something to be, the faster it has to spin. The faster it spins, the harder it is for the people inside to adjust.

So to get 1g of gravity, they found that a good in between would be about 4g of angular momentum. Astronauts could get used to that relatively easily in a few days. And that could be achieved in a spinning structure with the diameter equal to roughly the length of a football field. If they find that human health could be unaffected by living in lower gravity, say .5g, than you can decrease that size by 50%.

It's large. But not unreasonably so by any stretch. It's about the size of the ISS. Especially when you consider that it doesn't have to be a complete circle. If you can imagine a truss extending out from a central point like an aircraft propeller with a habitat on one end and a counterweight on the other. As someone else already mentioned, it's no different than building a suspension bridge.